Janet's children

I noticed today that in the list of characters for this series, the IMDb lists three children for Janet, played by Lucy Joyce, Julia Joyce, and Daniel Joyce. Now, I'm fairly sure that I was paying attention to the programme, and that Janet had just two children, played by the real-life sisters Lucy and Julia Joyce. I didn't see a male child, didn't see a Daniel Joyce listed in the credits at the end of the programme, and indeed can't find any reference anywhere else to an actor with that name.

So did I miss something, or is this just a completely fictitious credit?

If it is fictitious, I would be grateful if someone whose browser doesn't go wrong every time they try to submit information to the IMDb would do something about it. Thanks. :)